#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <cstring>

using namespace std;
// ascending order
#define vsort(v) sort(v.begin(), v.end())
// descending order
#define vsort_r(v) sort(v.begin(), v.end(), greater<int>())
#define vunique(v) unique(v.begin(), v.end())
#define mp make_pair
#define ts(x) to_string(x)
#define rep(i, a, b) for(int i = (int)a; i < (int)b; i++)
#define repm(i, a, b) for(int i = (int)a; i > (int)b; i--)
#define bit(a) bitset<8>(a)
#define des_priority_queue priority_queue<int, vector<int>, greater<int> >
#define all(v) (v).begin(), (v).end()
typedef long long ll;
typedef pair<int, int> P;
const ll INF = 1e18;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	// dp[i][j] : i, j番目まででの最小コスト
	// dp[i + 1][j + 1] = dp[i][j] + c[i][j]
	// 					  dp[i + 1][j] + c[i][j]
	// 					  dp[i][j + 1] + c[i][j]
	int n, m;
	cin >> n >> m;
	string S, T;
	cin >> S >> T;

	int dp[n + 1][m + 1];
	int inf = 1<<29;
	rep(i, 0, n + 1) rep(j, 0, m + 1) dp[i][j] = inf; 
	dp[0][0] = 0;
	rep(i, 0, n + 1) dp[i][0] = i;
	rep(j, 0, m + 1) dp[0][j] = j;

	rep(i, 0, n) rep(j, 0, m) {
		if(S[i] == T[j]) {
			dp[i + 1][j + 1] = min(dp[i + 1][j + 1], min(dp[i][j], min(dp[i + 1][j] + 1, dp[i][j + 1] + 1)));
		} else {
			dp[i + 1][j + 1] = min(dp[i + 1][j + 1], min(dp[i][j] + 1, min(dp[i + 1][j] + 1, dp[i][j + 1] + 1)));
		}
	}
	cout << dp[n][m] << endl;


}